As information terminal equipments such as personal computers, portable phones and the like are diffused, a reduction in a size and an increase in a density of printed wiring boards mounted in the above equipments are expedited. A mounting form thereof proceeds from a pin insertion type to a surface mount type and proceeds further to an area array type represented by BGA (ball grid array) in which a plastic substrate is used. In circuit boards on which bare chips are directly mounted as is the case with BGA, the chips are connected usually with the circuit boards by wire bonding carried out by thermal supersonic pressure bonding. In the thermal supersonic pressure bonding, circuit boards on which bare chips are mounted are exposed to a high temperature of 150° C. or higher. Accordingly, a heat resistance which can endure a temperature condition in the thermal supersonic pressure bonding is required for electrically insulating resins.
Further, a so-called repairing property in which a chip once mounted is detached from a substrate is required in a certain case. When a chip is detached from a substrate, heat of the same extent as in mounting a chip is applied. Also, when a chip is mounted again on a substrate, it is subjected further to heat treatment. The above repeated heating brings about separation between a fibrous base material of a prepreg and a resin in a certain case in conventional insulating resin systems. A durability (thermal shock resistance) against repeated exposure to high temperature is required to a substrate to which a repairing property is required.
A flame retardance of an epoxy resin can be ensured by adding halogen compounds containing halogen elements such as bromine and the like to it, but carbon monoxide, hydrogen cyanide and the like are generated in a certain case. Further, in epoxy resins to which halogen compounds such as bromine and the like are added, bromine can be decomposed in heating to bring about a reduction in a heat resistance and a reliability. Accordingly, molded articles in which a flame retardance can be ensured without adding halogen compounds to epoxy resins have been desired to be developed.
A method for ensuring a flame retardance without adding halogen compounds includes methods in which fillers such as nitrogen, silicon, aluminum hydroxide and the like are blended. Among them, a method in which phosphorus compounds are blended is widely used. For example, triphenyl phosphate (TPP) and tricresyl phosphate (TCP) which are compounds of a phosphoric acid ester base are used (refer to, for example, a patent document 1). However, when the above phosphorus compounds are added to epoxy resins, they are not reacted with the epoxy resins, and therefore the problem that the resulting molded articles are reduced in a heat resistance, a chemical resistance and the like after absorbing moisture has been brought about.
In contrast with this, a method in which an epoxy resin is reacted with a phosphorus compound to synthesize a phosphorus-containing epoxy resin has been proposed (refer to, for example, a patent document 2). However, dicyandiamide (DICY) is used as a curing agent, and therefore the problem that solvents such as dimethylformamide (DMF), dimethylacetamide (DMAc) and the like which burden a high load to the environment can not help being used has been involved therein. Also, it has not necessarily been able to sufficiently meet a low hygroscopicity, a thermal shock resistance and the like which are required recently.
Further, listed as well are, for example, methods in which phosphorus compounds such as 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide (trade name: HCA-HQ, manufactured by Sanko Co., Ltd.), 10-(2,5-dihydroxynaphthyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide (trade name: HCA-NQ, manufactured by Sanko Co., Ltd.) and derivatives thereof are used as curing agents.
However, the above curing agents have a low solubility in solvents and therefore require pre-reaction, and the problem that the handling property is reduced in terms of complicating the production process has been involved therein.